SEATTLE -- Central auditory testing may act as an early screen for cognitive decline in the elderly, researchers here said.

Action Points

Explain to interested patients that, according to this study, problems with central auditory processing reflect cognitive decline and may serve as a measure of early dementia.

Explain that the correlation was not perfect and applies only to this particular type of hearing problem.

Explain that the central processing tests are relatively simple and, in patients reporting hearing loss, may be helpful in determining if a hearing aid will be beneficial.

SEATTLE, July 21 -- Central auditory testing may act as an early screen for cognitive decline in the elderly, researchers here said.

In a study of 313 patients at least 71 years old, several measures of central auditory processing were impaired in those diagnosed with Alzheimer's disease and, to a lesser extent, those with memory impairment but not meeting criteria for Alzheimer's, reported George A. Gates, M.D., of the University of Washington, and colleagues in the July issue of Archives of Otolaryngology and Head and Neck Surgery.

Central auditory processing is the brain function involved in interpreting complex sounds such as speech.

Such hearing problems often show up as an inability to understand speech against a background of other conversations, sometimes called the "cocktail party effect." Amplification with hearing aids does not help this form of auditory defect.

Dr. Gates recommended that central processing tests be performed routinely in older patients who say they are experiencing hearing loss.

A negative finding on the central test, he said, can reassure the patient as well as verify that a hearing aid may help.

Earlier research had found central auditory processing dysfunctions in patients with dementia and documented memory impairments, Dr. Gates said.

The new study confirms those findings and suggested that central auditory testing could be a simple screening tool for cognitive decline, he said.

Not only could testing help patients receive the most appropriate therapy for the hearing problem, but it could also identify those at high risk for dementia, he said.

Participants in the study underwent testing with three measures of central auditory processing, each scored on a 100-point scale.

In one, listeners were asked to identify which one of 10 nonsense sentences were presented against a background of an interesting narrative given by the same speaker.

The second test involved delivering different sentences to each ear simultaneously, with listeners then selecting which they heard from a printed list.

The third test was similar to the second except that numbers were delivered to each ear.

Participants were also evaluated for peripheral hearing loss with pure-tone threshold tests and other standard measures.

The sample included 232 patients with no signs of cognitive deficit, 64 with mild memory impairment without dementia, and 17 with Alzheimer's.

After adjusting for age and performance on the peripheral hearing tests, Dr. Gates and colleagues found that mean performance on the three central processing tests was significantly poorer among those with mild impairment relative to controls, and poorer still among those with Alzheimer's.

For example, mean scores on the first test (recognizing sentences delivered against the narrative background) were 76.5 (SD 22.7) for controls, 50.4 (SD 28.5) for those with mild impairment without dementia, and 29.8 (SD 30.5) for those with Alzheimer's disease.

The researchers found a similar pattern in the other central processing tests. In all cases, scores for those with memory impairments (with or without dementia) were significantly lower than for controls.

"Given that about half of older adults with isolated memory loss progress to frank dementia, identifying early cases has considerable merit," Dr. Gates and colleagues wrote.

They said the central processing tests "are relatively simple to administer because standardized, prerecorded materials are used."

The tests are also more pleasant and non-threatening than some cognition tests, the researchers said.

Mean scores for the memory-impaired without dementia did not differ significantly from those for patients with Alzheimer's disease, because of substantial variability in test results within each group.

Dr. Gates and colleagues acknowledged "considerable heterogeneity" in their results. Some showed central processing impairment on one test but not others; some with cognitive impairments scored normal on all three tests; and some control participants had low scores on one or more tests.

When scores on the three tests were combined into a single composite, it had a sensitivity of 80.2% and specificity of 78.4% in discriminating those with cognitive impairments from controls.

The individual tests were not quite as accurate by themselves. For example, the second test (different sentences fed into each ear) had 52.5% sensitivity and 93.5% specificity when a score of 50 was used as a cutoff.

When the cutoff was set at 80 instead, the sensitivity improved to 83.8%, but specificity was reduced to 57.6%.

But the researchers said the improvement in accuracy offered by the composite would have to balance against the time needed to administer all three tests.

Dr. Gates said he would recommend an approach using a very low score as the cutoff. Patients showing such severe central defects would then see a neurologist for more detailed cognitive testing.

A limitation of central processing testing is that many older patients do not have the vision or peripheral hearing function required by the test protocols, the researchers said.

Another paper from the same group has been accepted by Ear and Hearing for publication this fall, Dr. Gates said.

It will report that central processing defects progress faster than peripheral hearing loss in people over 70.

"This leads me to believe that it is the brain effect on hearing that is the major problem in the elderly and wearing a hearing aid does not help," he said.

He said central processing defects can be treated. Training programs have been developed that help patients listen more carefully to improve their comprehension.

The study was supported by the National Institute of Deafness and Other Communication Disorders and the National Institute on Aging. No potential conflicts of interest were reported.

Reviewed by Zalman S. Agus, MD Emeritus Professor University of Pennsylvania School of Medicine

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